Sensitive luminescence mechanochromism and unique luminescence thermochromism tuned by bending the P–O–P skeleton in the diphosphonium/iodocuprate(i) hybrid

Abstract

Two new copper(I) iodide-based hybrids, i.e. (Py₃P–O–PPy₃)(Cu₂I₄) (1) and (Py₃P–O–PPy₃)(Cu₄I₆) (2) (Py = pyrrolidine), have been prepared, in which the tripodal diphosphonium (Py₃P–O–PPy₃)²⁺ is in situ generated in the one-pot synthesis. The disordered (Cu₄I₆)²⁻ tetramers are rare with two sets of tetracuprate centers. Interestingly, 1 exhibits sensitive luminescence mechanochromism, which is ascribed to the disturbed cuprophilic Cu⋯Cu interactions and the crystalline packing adjustment by destroying C–H⋯I hydrogen bonds during mechanical force. In particular, the luminescence thermochromism is unique, whose fluorescence intensity is strengthened with the elevated temperature. This could be due to the S₂–S₁ internal conversion on the linear P–O–P backbone, which will be bent upon heating. Simultaneous luminescence thermo/mechanochromism can also be monitored in 1. However, no luminescence thermo/mechanochromic performances can be detected in 2, so the luminescence thermo/mechanochromism of 1 could be quenched with DMF. The conclusions in this work might provide a new large-scale synthesis strategy for intelligent responsive luminescent materials.